The present application relates generally to photoresist materials, and more particularly, to photoresist compositions that can be utilized for lithography at 157 nm.
Photolithography employs photoresists, i.e., radiation sensitive resist materials, for transfer of images onto semiconductor wafers to selectively pattern the wafers for device manufacturing. For example, spin-on organic polymeric photoresists have enabled manufacturing of integrated circuits.
Recent advances in microlithographical techniques lay the foundation for performing lithography at sub-100 nm wavelengths. A wide variety of energy sources, such as X-rays, extreme ultra violet (EUV), low and high keV electrons, ion beams, and extended optical wavelengths, e.g., 157 nm, can potentially be employed for advanced sub-100 nm imaging. For example, lithography with 157 nm F2 lasers represents the next evolutionary step in optical micro-lithography and has recently emerged as a promising candidate for the 100 run and 70 nm lithographical applications.
The resist materials developed for longer wavelengths, however, are too absorbent to be useful as single layer resists at such low wavelengths, e.g., at 157 nm. For example, polyhydroxystyrene based resists, developed for 248 nm lithography, and polyacrylate and polycyclic copolymer based resists, developed for 193-nm lithography, are too absorbent to provide a single layer resist having a thickness of 150 nm or more for use at 157 nm. A photoresist based on such polymers may be useful for 157 nm lithography only if the thickness of the resist is less than about 100 nm. This constraint on thickness can seriously compromise the resist""s ability to perform its intended purpose. For example, such a resist may be too thin to withstand subsequent processing steps such as plasma etching and ion implantation.
Thus, a need exists for providing photoresists for use in microlithography, and in particular, for use at 157 nm wavelength. More particularly, a need exists for providing single layer photoresists for use at 157 nm.
The present invention provides photoresists for use in lithography at wavelengths less than about 248 nm, and more particularly, at wavelengths about 157 nm. In one aspect, a photoresist composition of the invention includes a polymer having at least one monomeric unit with an aromatic moiety. The monomeric unit further includes at least a group attached to the aromatic moiety. The attached group has at least one CF bond. The polymer further includes an acidic hydroxyl group. A photoresist of the invention has relatively low absorbance at wavelengths less than about 248 nm, e.g., absorbance in a range of 1-5 xcexcmxe2x88x921, and more preferably in a range of 2-4 xcexcmxe2x88x921 at 157 nm, which allows production of single layer resists at these wavelengths with sufficient thickness to be suitable for photolithography.
In one aspect, a photoresist of the invention includes a homopolymer having a chemical formula:
[-A-A-]n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In another aspect, a photoresist of the invention includes a copolymer having a chemical formula:
[-A-Axe2x80x2-]n
where A and Axe2x80x2 are two different hexafluoroisopropanol styrene moieties. For example, A can be 2-hexafluoroisopropanol styrene and Axe2x80x2 can be 3-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In related aspect, a photoresist of the invention can include a copolymer having a chemical formula:
[-A-B-]n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
B=2,3, or 4-t-butoxycarbonyl-hexafluoroisopropanol styrene, 2,3, or 4-t-butyl acetate-hexafluoroisopropanol styrene, 2,3, or 4-methoxymethoxy-hexafluoroisopropanol styrene, t-butyl acrylate, t-butyl methacrylate, or t-butyl trifluoromethacrylate.
The molar concentration of the monomeric unit A is in a range of about 40-100%, and more preferably in a range of about 50-80%, and the molar concentration of the monomeric unit B is in a range of about 0-60%, and more preferably in a range of 20-50%. Further, the polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In another aspect, a photoresist of the invention can include a copolymer having a chemical formula:
[-A-C-]n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
C=styrene, 4-t-butylstyrene, 2,3, or 4-fluorostyrene, 2,3,4,5,6-pentafluorostyrene, 2,3, or 4-trifluoromethylstyrene, 3,5-bis(trifluoromethyl)styrene, 2,3, or 4-hexafluoroisopropylstyrene, 2,3, or 4-trifluoroacetylstyrene, 2,3, or 4-heptafluorobutyrylstyrene, acrylonitrile, or methacrylonitrile.
The molar concentration of the monomeric unit A is in a range of about 40-100%, and more preferably in a range of about 50-80%, and the molar concentration of the monomeric unit C is in a range of about 0-60%, and more preferably in a range of 20-50%. Further, the polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons
In another aspect, a photoresist of the invention can include a terpolymer having a chemical formula:
[-A-Axe2x80x2-Axe2x80x3-]n
where A is selected to be 2-hexafluoroisopropanol styrene, and Axe2x80x2 is selected to be 3-hexafluoroisopropanol styrene, and Axe2x80x3 is selected to be 4-hexafluoroisopropanol styrene. The polymer can have a molecular weight in a range of about 5000 to 100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons
Another photoresist according to the invention can include a terpolymer having a chemical formula:
[-A-B-C-]n
where
A=2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, or 4-hexafluoroisopropanol styrene, and
B=2,3, or 4-t-butoxycarbonyl-hexafluoroisopropanol styrene, 2,3, or 4-t-butyl acetate-hexafluoroisopropanol styrene, 2,3, or 4-methoxymethoxy-hexafluoroisopropanol styrene, t-butyl acrylate, t-butyl methacrylate, t-butyl trifluoromethacrylate, and
C=styrene, 4-t-butylstyrene, 2,3, or 4-fluorostyrene, 2,3,4,5,6-pentafluorostyrene, 2,3, or 4-trifluoromethylstyrene, 3,5-bis(trifluoromethyl)styrene, 2,3, or 4-hexafluoroisopropylstyrene, 2,3, or 4-trifluoroacetylstyrene, 2,3, or 4-heptafluorobutyrylstyrene, acrylonitrile, or methacrylonitrile.
The molar concentration of A is selected to be in a range of about 40-100%, and more preferably in a range of 50-80%, and the molar concentration of B is selected to be in a range of 0-60%, and more preferably in a range of 20-50%. Further, the molar concentration of C is selected to be in a range of about 0-50%, and more preferably in a range of about 0-30%. The polymer has a molecular weight in a range of about 5000-100,000 Daltons, and more preferably in a range of 5000 to 30,000 Daltons.
In addition to the polymers described above, a photoresist composition of the invention can also contain a small amount of base which may help to stabilize the polymer system. In general, less than 1% of the polymer composition is a base component, based on the total weight of the polymer composition, e.g., less than 0.5%. Suitable bases typically are organic bases known in the art such as tetrabutylammonium hyroxide, diazabicyclo[5.4.0]undec-7-ene, diphenyl amine, trioctyl amine, or triheptyl amine.
Further, a photoresist composition of the invention can include a photoacid generator. The term xe2x80x9cphoto-acid generatorxe2x80x9d is recognized in the art and is intended to include those compounds which generate acid in response to radiant energy. Preferred photoacid generators for use in the present invention are those that are reactive to deep UV radiation, e.g., to radiant energy having a wavelength equal to or less than 248 nm, and are preferably highly reactive to radiation at 157 nm. The combination of the photo-acid generator and polymer should be soluble in an organic solvent. Preferably, the solution of the photo-acid generator and polymer in the organic solvent are suitable for spin coating. The photo-acid generator can include a plurality of photo-acid generators. The photo-acid generator is included in the composition at levels between about 0.01% and about 50%, more preferably between about 0.5% and about 20%, and most preferably between about 1.0% and about 10%, based on the total weight of the polymer composition.
Suitable photo-acid generators include onium salts, such as triphenylsulfonium salts, sulfonium salts, iodonium salts, diazonium salts and ammonium salts, 2,6-nitrobenzylesters, aromatic sulfonates, sulfosuccinimides and photosensitive organic halogen compounds as disclosed in Japanese Examined Patent Publication No. 23574/1979.
Examples of diphenyliodonium salts include diphenyliodonium triflate (DPI-105, Midori Kagaku Co. Ltd.) and diphenyliodonium tosylate (DPI-201, Midori Kagaku Co. Ltd.). Examples of suitable bis(4-tert-butylphenyl)iodonium salts include bis(4-tert-butylphenyl)iodonium triflate (BBI-105, Midori Kagaku Co. Ltd.), bis(4-tert-butylphenyl)iodonium camphorsulfate (BBI-106, Midori Kagaku Co. Ltd.), bis(4-tert-butylphenyl)iodonium perfluorbutylate (BBI-109, Midori Kagaku Co. Ltd.) and bis(4-tert-butylphenyl)iodonium tosylate (BBI-201, Midori Kagaku Co. Ltd.). Suitable examples of triphenylsulfonium salts include triphenylsulfonium hexafluorophosphate (TPS-102, Midori Kagaku Co. Ltd.), triphenylsulfonium triflate (TPS-105, Midori Kagaku Co. Ltd.) and triphenylsulfonium perfluorobutylate (TPS-109, Midori Kagaku Co. Ltd.). An example of an aromatic sulfonate is 1,2,3-tri(methanesulfonyloxy)benzene.
Specific examples of the photosensitive organic halogen compound include halogen-substituted paraffinic hydrocarbons such as carbon tetrabromide, iodoform, 1,2,3,4-tetrabromobutane and 1,1,2,2-tetrabromoethane; halogen-substituted cycloparaffinic hydrocarbons such as hexabromocyclohexane, hexachlorocyclohexane and hexabromocyclododecane; halogen-containing s-triazines such as tris(trichloromethyl)-s-triazine, tris(tribromomethyl)-s-triazine, tris(dibromomethyl)-s-triazine and 2,4-bis(tribromomethyl)-6-methoxyphenyl-s-triazine; halogen-containing benzenes such as (bis(trichloromethyl)benzene and bis(tribromomethyl)benzene; halogen-containing sulfone compounds such as tribromomethylphenylsulfone, trichloromethylphenylsulfone and 2,3-dibromosulforane; and halogen-substituted isocyanurates such as tris(2,3-dibromopropyl)isocyanurate. Among such photosensitive organic halogen compounds, a bromine-containing compound is particularly preferred.
In another aspect, a polymer of a photoresist composition of the invention includes carbon atoms bearing protected hydroxyl groups, and the protecting groups are labile in the presence of in situ generated acid. The term xe2x80x9cprotected hydroxyl groupxe2x80x9d is well recognized in the art and is intended to include those groups which are resistant to basic solutions but are removed under acidic conditions. The hydroxyl groups of the polymer can be protected by chemical reactions by using protecting groups which render the reactive hydroxyl groups substantially inert to the reaction conditions. (See for example, Protective Groups in Organic Synthesis, 2 ed., T. W. Green and P. G. Wuts, John Wiley and Sons, New York, N.Y. 1991). Thus, for example, protecting groups such as the following may be utilized to protect hydroxyl groups: acetals, ketals, esters, e.g., t-butyl esters, and ethers known in the art; trialkyl silyl groups, such as trimethylsilyl and t-butyldimethylsilyl (TBDMS); and groups such as trityl, tetrahydropyranyl, vinyloxycarbonyl, o-nitrophenylsulfonyl, diphenylphosphinyl, p-toluenesulfonyl, and benzyl, may all be utilized. Additionally, CH3OCH2Cl, (CH3)3SiCH2CH2OCH2Cl, CH3OCH2CH2OCH2Cl, ClCO2-t-butyl, methyl dihydropyran, methyl dihydrofuran, tetrabutylvinylether, 2-methoxypropene, isobutylvinylether and ethylvinylether are useful as protecting groups. (See for example, C. Mertesdor et al. Microelectronics Technology, 1995, pg. 35-55.)
The protecting group may be removed, after completion of the synthetic reaction of interest, by procedures known to those skilled in the art. For example, acetal and ketal groups may be removed by acidolysis, the trityl group by hydrogenolysis, TBDMS by treatment with fluoride ions, and TCEC by treatment with zinc. One skilled in the art will appreciate that the choice of a hydroxyl protecting group(s) is tailored to the specific application and conditions to which the protected hydroxyl group must withstand. Ultimately, the generation of acid from the photo-acid will cleave the oxygen bond to the protecting group to regenerate a free hydroxyl group.
An interaction between an energy source, e.g. a source that generates 157 nm radiation, and the photo-acid generator results in the release of acid which facilitates selective cleavage of protecting groups from hydroxyl sites. As a consequence, the resultant unprotected hydroxyl groups are susceptible to solubilization under basic conditions, i.e., the regions of the photoresist material that are exposed to the far UV radiation are rendered alkali soluble, whereas the unexposed (protected hydroxyl) regions of the photoresist material remain alkali insoluble. Suitable protecting groups for the hydroxyl groups of the polymer include acetals, ketals, esters (including carbonates) and ethers.
In addition to the hydroxyl protected polymer and photo-acid generator, small molecules which help to inhibit hydrolysis of the protected hydroxyl groups can be included in the compositions of the invention. These small molecules are typically ester, ether, ketal or acetal protected low molecular weight polyhydridic alcohols or low molecular weight alcohols. The protecting groups can further include those listed below. Suitable low molecular weight hydrolysis inhibitors include, for example, Di-Boc Bisphenol A, Di-Boc o-cresolphthalein, tert-butyl lithocholate and tert-butyl deoxycholate (available from Midori Kagaku Co., Ltd. Tokyo, Japan).
Thus the above described compositions include protected hydroxyl groups which are labile in the presence of in situ generated acid. Upon exposure to a far UV energy source, e.g. a source which generates 157 nm radiation, the photo-acid generator will release acid to facilitate selective cleavage of protecting groups from protected hydroxyl sites. As a consequence, the resultant unprotected hydroxyl groups will be susceptible to solubilization under basic conditions and the exposed photoresist material is rendered alkali soluble, whereas the unexposed photoresist material will remain alkali insoluble.
In another aspect, the invention provides a single layer 157 nm sensitive photoresist, which includes a photoresist composition having a polymer with at least one monomeric unit with an aromatic moiety. The monomeric unit can further include a group, such as an electron withdrawing group, having at least one CF bond attached to the aromatic moiety.
A single layer 157 nm sensitive photoresist according to the invention can have an absorbance at 157 nm in a range of about 1-5 xcexcmxe2x88x921. More preferably, the photoresist has an absorbance in a range of approximately 2-4 xcexcmxe2x88x921. Such an absorbance allows production of single layer resists having a thickness in range of approximately 50 to 300 nm 1 and more preferably in a range of 100 nm to 150 nm, for use in 157 nm lithography.
According to a related aspect, a single layer resist of the invention for use in 157 nm lithography can include a copolymer or a terpolymer having a monomeric unit that can be selected to be, for example, 4-trifluoromethyl styrene, 3,5-bis(trifluoromethyl) styrene, 4-hexafluoroisopropyl styrene, 4-trifluoroacetyl styrene, 4-heptafluorobutyrylstyrene, 2-hexafluoroisopropanol styrene, 3-hexafluoroisopropanol styrene, 4-hexafluoroisopropanol styrene, 4-t-butoxycarbonyl-hexafluoroisopropanol styrene, 4-t-butyl acetate-hexafluoroisopropanol styrene, and 4-methoxymethoxy-hexafluoroisopropyl styrene.
These and other aspects of the invention can be better understood by reference to the following detailed description and the appended claims.